1. Field of the Invention
This invention relates to a simulator for automatic photographic printers, and more particularly relates to a simulator for automatic photographic printers adapted to display on a CRT an image that is the same as that of a final print to be printed on be printing paper sheet by means of an automatic color photographic printer.
2. Description of the Related Art
It is well known in the art to employ an automatic color photographic printer which is capable of performing printing and developing in such a manner that the density and color balance of all the final prints are the same, irrespective of the extent of shading on the negative film (underexposure, proper exposure, overexposure). This is done by measuring the cumulative transmission density (LATD) to correct the density and by conducting slope control. Such an automatic color photographic printer includes an optical system comprising a light source, a dimmer filter, a mirror chamber, a negative carrier and a black shutter, arranged in succession. Printing with such a printer is effected as follows first, a color negative film is set on the negative carrier, and the light source is turned on. Then the black shutter is opened to allow the image on the negative film to be focused on a paper sheet for printing and be printed thereon. The final print can then be automatically obtained by developing the printing paper sheet through a development process. In this automatic photographic printer, a photocell resolves a light beam transmitted through a negative film into the three primary color rays, red (R), green (G) and blue (B), to perform density control using the LATD in accordance with Evans's Theorem. At the same time, color balance is controlled by performing slope control in such a manner that slope agreement may be attained for the three primary colors. Consequently, this automatic color photographic printer enables all final prints to be obtained with the same density and color balance.
However, even when the main subject is properly exposed, a high or low background density may give rise to a density problem, the exposure being controlled under the influence of the background density. Further, when the color balance of the main subject differs from that of the background, which is the case, for example, when the color of the main subject and that of the background have a complementary relationship, a color failure may be generated. Accordingly, the quality of the final print may be poor even when the density and slope control are performed. Such a poor print quality requires that the printing and development be conducted PG,4 again.
To cope with this problem, what is called a photographic tester has been put in use, as is disclosed in Japanese Patent Laid-Open No. 46731/78. Such a photographic tester includes a simulator which is adapted to display the image of a negative film picked up by a television camera on a television screen, and which, while thus displaying the image, adjusts the color video signal in such a manner that the desired density and color balance are obtained. Printing is performed by an automatic photographic printer using the color video signal thus adjusted. In another simulator, which is disclosed in Japanese Patent Publication No. 25220/67, the image of a negative film to be printed on a printing paper sheet is displayed on a television screen, and an automatic exposure device is connected with the resistance to enable brightness and contrast adjustment of the television picture. In this way, picture simulation can be performed so that the necessity for repeating printing and development operations may be eliminated as much as possible.
Since, however, the gamma of a conventional television is approximately 2.2, a gamma correction circuit of gamma=0.45 is incorporated in the camera so that the gamma of the entire device may be 1. On the other hand, prints are usually finished with gamma=2.0 since a high-contrast finish is preferable in appearance. Thus it has been necessary to provide in the simulator a gamma correction circuit of gamma=2.0 to conduct a gamma correction corresponding to the gamma characteristics of the printing paper used. This results in the gamma of the color negative film (about 0.6) being both decreased by the gamma correction circuit of the camera and increased by that in the simulator, which leads to deterioration of the SN ratio and the television image quality. The construction also involves a rather high production cost because it requires two gamma correction circuits, gamma correction being effected both in the camera and in the simulator.